linux-hardening - Re: [PATCH 5/6] driver core: Add __alloc

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Date:   Thu, 2 Feb 2023 12:11:47 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        John Stultz <jstultz@...gle.com>,
        Yongqin Liu <yongqin.liu@...aro.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Gunthorpe <jgg@...pe.ca>, Nishanth Menon <nm@...com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Won Chung <wonchung@...gle.com>,
        David Gow <davidgow@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-hardening@...r.kernel.org,
        llvm@...ts.linux.dev, Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [PATCH 5/6] driver core: Add __alloc_size hint to devm allocators

On Thu, Feb 2, 2023 at 11:53 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Thu, Feb 02, 2023 at 11:49:42AM -0800, Sami Tolvanen wrote:
> > A quick look at Clang's source code suggests that Intrinsic::ubsantrap
> > already accepts the handler ID (from the SanitizerHandler enum) as an
> > argument and the arm64 LLVM back-end appears to encode the value as an
> > immediate for the brk instruction. I didn't confirm that this actually
> > works, but perhaps we just need to teach the kernel about the possible
> > values?
>
> Oh excellent. Yeah, if that's all that's needed here that would be
> great. What are the values?

The arm64 brk immediate encoding seems to be "ubsantrap arg | 'U' << 8":

https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AArch64/AArch64InstrInfo.td#L7571

The argument values come from the SanitizerHandler enum, which is
populated from this list:

https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CodeGenFunction.h#L113

Therefore, according to the tests, for ubsantrap(12) we'll get brk
#0x550c, for example:

https://github.com/llvm/llvm-project/blob/main/llvm/test/CodeGen/AArch64/ubsantrap.ll

Sami